.TH "asn1 parsing and datatype manipulation routines." 3 "30 Jun 2005" "Version 5.2.1.rc3" "net-snmp" \" -*- nroff -*-
.ad l
.nh
.SH NAME
asn1 parsing and datatype manipulation routines. \- 
.SS "Defines"

.in +1c
.ti -1c
.RI "#define \fBNULL\fP   0"
.br
.in -1c
.SS "Functions"

.in +1c
.ti -1c
.RI "int \fBasn_check_packet\fP (u_char *pkt, size_t len)"
.br
.ti -1c
.RI "u_char * \fBasn_parse_int\fP (u_char *data, size_t *datalength, u_char *type, long *intp, size_t intsize)"
.br
.ti -1c
.RI "u_char * \fBasn_parse_unsigned_int\fP (u_char *data, size_t *datalength, u_char *type, u_long *intp, size_t intsize)"
.br
.ti -1c
.RI "u_char * \fBasn_build_int\fP (u_char *data, size_t *datalength, u_char type, const long *intp, size_t intsize)"
.br
.ti -1c
.RI "u_char * \fBasn_build_unsigned_int\fP (u_char *data, size_t *datalength, u_char type, const u_long *intp, size_t intsize)"
.br
.ti -1c
.RI "u_char * \fBasn_parse_string\fP (u_char *data, size_t *datalength, u_char *type, u_char *string, size_t *strlength)"
.br
.ti -1c
.RI "u_char * \fBasn_build_string\fP (u_char *data, size_t *datalength, u_char type, const u_char *string, size_t strlength)"
.br
.ti -1c
.RI "u_char * \fBasn_parse_header\fP (u_char *data, size_t *datalength, u_char *type)"
.br
.ti -1c
.RI "u_char * \fBasn_parse_sequence\fP (u_char *data, size_t *datalength, u_char *type, u_char expected_type, const char *estr)"
.br
.ti -1c
.RI "u_char * \fBasn_build_header\fP (u_char *data, size_t *datalength, u_char type, size_t length)"
.br
.ti -1c
.RI "u_char * \fBasn_build_sequence\fP (u_char *data, size_t *datalength, u_char type, size_t length)"
.br
.ti -1c
.RI "u_char * \fBasn_parse_length\fP (u_char *data, u_long *length)"
.br
.ti -1c
.RI "u_char * \fBasn_build_length\fP (u_char *data, size_t *datalength, size_t length)"
.br
.ti -1c
.RI "u_char * \fBasn_parse_objid\fP (u_char *data, size_t *datalength, u_char *type, oid *objid, size_t *objidlength)"
.br
.ti -1c
.RI "u_char * \fBasn_build_objid\fP (u_char *data, size_t *datalength, u_char type, oid *objid, size_t objidlength)"
.br
.ti -1c
.RI "u_char * \fBasn_parse_null\fP (u_char *data, size_t *datalength, u_char *type)"
.br
.ti -1c
.RI "u_char * \fBasn_build_null\fP (u_char *data, size_t *datalength, u_char type)"
.br
.ti -1c
.RI "u_char * \fBasn_parse_bitstring\fP (u_char *data, size_t *datalength, u_char *type, u_char *string, size_t *strlength)"
.br
.ti -1c
.RI "u_char * \fBasn_build_bitstring\fP (u_char *data, size_t *datalength, u_char type, const u_char *string, size_t strlength)"
.br
.ti -1c
.RI "u_char * \fBasn_parse_unsigned_int64\fP (u_char *data, size_t *datalength, u_char *type, struct counter64 *cp, size_t countersize)"
.br
.ti -1c
.RI "u_char * \fBasn_build_unsigned_int64\fP (u_char *data, size_t *datalength, u_char type, const struct counter64 *cp, size_t countersize)"
.br
.ti -1c
.RI "int \fBasn_realloc\fP (u_char **pkt, size_t *pkt_len)"
.br
.in -1c
.SH "Detailed Description"
.PP 
Note on
.PP
Re-allocating reverse ASN.1 encoder functions. Synopsis:
.PP
.PP
.nf
 u_char *buf = (u_char*)malloc(100);
 u_char type = (ASN_UNIVERSAL | ASN_PRIMITIVE | ASN_INTEGER);
 size_t buf_len = 100, offset = 0;
 long data = 12345;
 int allow_realloc = 1;
 
 if (asn_realloc_rbuild_int(&buf, &buf_len, &offset, allow_realloc,
                            type, &data, sizeof(long)) == 0) {
     error;
 }
.fi
.PP
.PP
NOTE WELL: after calling one of these functions with allow_realloc non-zero, buf might have moved, buf_len might have grown and offset will have increased by the size of the encoded data. You should **NEVER** do something like this:
.PP
.PP
.nf
 u_char *buf = (u_char *)malloc(100), *ptr;
 u_char type = (ASN_UNIVERSAL | ASN_PRIMITIVE | ASN_INTEGER);
 size_t buf_len = 100, offset = 0;
 long data1 = 1234, data2 = 5678;
 int rc = 0, allow_realloc = 1;
 
 rc  = asn_realloc_rbuild_int(&buf, &buf_len, &offset, allow_realloc,
                                type, &data1, sizeof(long));
 ptr = buf[buf_len - offset];   / * points at encoding of data1 * /
 if (rc == 0) {
      error;
 }
 rc  = asn_realloc_rbuild_int(&buf, &buf_len, &offset, allow_realloc,
                              type, &data2, sizeof(long));
 make use of ptr here;
.fi
.PP
.PP
ptr is **INVALID** at this point. In general, you should store the offset value and compute pointers when you need them:
.PP
.PP
.nf
 u_char *buf = (u_char *)malloc(100), *ptr;
 u_char type = (ASN_UNIVERSAL | ASN_PRIMITIVE | ASN_INTEGER);
 size_t buf_len = 100, offset = 0, ptr_offset;
 long data1 = 1234, data2 = 5678;
 int rc = 0, allow_realloc = 1;
 
 rc  = asn_realloc_rbuild_int(&buf, &buf_len, &offset, allow_realloc,
                              type, &data1, sizeof(long));
 ptr_offset = offset;
 if (rc == 0) {
      error;
 }
 rc  = asn_realloc_rbuild_int(&buf, &buf_len, &offset, allow_realloc,
                              type, &data2, sizeof(long));
 ptr = buf + buf_len - ptr_offset
 make use of ptr here;
.fi
.PP
.PP
Here, you can see that ptr will be a valid pointer even if the block of memory has been moved, as it may well have been. Plenty of examples of usage all over \fBasn1.c\fP, \fBsnmp_api.c\fP, \fBsnmpusm.c\fP.
.PP
The other thing you should **NEVER** do is to pass a pointer to a buffer on the stack as the first argument when allow_realloc is non-zero, unless you really know what you are doing and your machine/compiler allows you to free non-heap memory. There are rumours that such things exist, but many consider them no more than the wild tales of a fool.
.PP
Of course, you can pass allow_realloc as zero, to indicate that you do not wish the packet buffer to be reallocated for some reason; perhaps because it is on the stack. This may be useful to emulate the functionality of the old API:
.PP
.PP
.nf
 u_char my_static_buffer[100], *cp = NULL;
 size_t my_static_buffer_len = 100;
 float my_pi = (float)22/(float)7;
 
 cp = asn_rbuild_float(my_static_buffer, &my_static_buffer_len,
                       ASN_OPAQUE_FLOAT, &my_pi, sizeof(float));
 if (cp == NULL) {
 error;
 }
.fi
.PP
.PP
IS EQUIVALENT TO:
.PP
.PP
.nf
 u_char my_static_buffer[100];
 size_t my_static_buffer_len = 100, my_offset = 0;
 float my_pi = (float)22/(float)7;
 int rc = 0;
 
 rc = asn_realloc_rbuild_float(&my_static_buffer, &my_static_buffer_len,
                               &my_offset, 0,
                               ASN_OPAQUE_FLOAT, &my_pi, sizeof(float));
 if (rc == 0) {
   error;
 }
.fi
.PP
 
